PET Preform Manufacturing: From Injection Molding to Blowing

Have you ever wondered how PET preforms are made before they become bottles? Understanding the process helps you make better choices when selecting suppliers or customizing packaging for your cosmetic brand.

PET preform manufacturing starts with injection molding, where melted PET resin is shaped into tube-like preforms. These preforms are later reheated and stretched in a blow molding machine to form final bottles or jars. The two-step process ensures shape precision, strength, and visual clarity.

Now let’s take a closer look at each phase of the process.

What Is the Role of Injection Molding in PET Preform Production?

Injection molding is the first step in making PET preforms. It involves melting PET pellets and injecting them into steel molds under high pressure. The result is a small, thick-walled plastic preform that resembles a test tube.

Each preform is built with specific:

• Neck size (e.g. 28mm PCO, 38mm wide mouth)
• Gram weight (usually 10g to 70g)
• Thread profile (to fit pumps, caps, or closures)

This step defines the foundation of your final cosmetic bottle.

What Materials Are Used for PET Preforms?

PET preforms are primarily made from:

• Virgin PET resin – For clear, stable, and premium packaging
• Recycled PET (rPET) – For eco-conscious brands
• PET with additives – Such as UV blockers or colorants (e.g., amber or frosted finishes)

Raw material quality impacts preform color, strength, and chemical resistance. Brands should always request material certificates from suppliers.

What Are the Key Steps in PET Preform Injection Molding?

Here’s a simplified overview of the injection process:

1. Drying PET resin – Removes moisture to avoid bubbles
2. Feeding resin into the barrel – Heated to ~270°C
3. Injecting into mold cavities – Shaped under pressure
4. Cooling – Hardened with water-cooled molds
5. Ejecting preforms – Transferred to conveyor for inspection

High-speed molding systems can make 16 to 96 preforms per cycle depending on the mold size.

How Does the Blow Molding Process Work After Preform Is Made?

Blow molding transforms preforms into bottles or jars:

1. Preform heating – Uniformly warms the preform, avoiding thermal stress
2. Stretching – A steel rod extends the preform lengthwise
3. Blowing – Compressed air expands it into the mold cavity
4. Cooling & release – The new bottle is released and trimmed

This is known as two-step blow molding, allowing more design flexibility than single-step methods. It’s common in cosmetics, beverages, and pharma.

What Machines Are Used in the PET Preform and Blowing Process?

For injection molding:

• PET Preform Injection Molding Machine – Brands like Husky, Demark, Haitian
• Dehumidifier – For drying PET pellets
• Mold Chiller – Maintains stable mold temperature
• Robot arm / auto-drop system – For mass production

For blow molding:

• Infrared preform heater
• Blow molding station (1-cavity to 6-cavity common)
• Neck alignment units – Ensures caps/pumps fit perfectly

Automation level affects both speed and consistency.

How to Ensure Quality Control During Preform Manufacturing?

Quality assurance is critical. Here’s what top-tier manufacturers check:

• Weight tolerance (±0.1g)
• Neck finish accuracy – Thread angle and diameter
• AA Level – Should be below 8 ppm for cosmetic use
• Visual inspection – No black dots, bubbles, or cracks
• Stress testing – For blowing consistency

For export customers, ask for:

• QC reports
• Preform samples
• Mold maintenance logs

Chinese suppliers like KGI Preforms offer batch QC reports for each shipment.

Conclusion

PET preform manufacturing is a precise process that transforms raw resin into the beautiful bottles you see on cosmetic shelves. Knowing the details helps you ask the right questions and choose reliable partners. Want help choosing a preform or machine? Leave a comment, and I’ll guide you through it.